Self-Expanding Cooling Electrode for Renal Nerve Ablation

ABSTRACT

A metallic tube arrangement includes an electrode region configured to expand radially and contract radially in response to increasing and decreasing a temperature at the electrode region, respectively. The electrode region is configured for intravascular deployment and delivery of high frequency energy to target tissue of a target vessel of the body. The electrode region is configured to expand radially to a diameter sufficient to contact an inner wall of the target vessel in response to a decrease in electrode region temperature and to contract radially to a diameter smaller than a diameter of the target vessel in response to an increase in electrode region temperature.

RELATED PATENT DOCUMENTS

This application claims the benefit of Provisional Patent ApplicationSer. Nos. 61/413,781 filed Nov. 15, 2010 and 61/491,730 filed May 31,2011, to which priority is claimed pursuant to 35 U.S.C. §119(e) andwhich are hereby incorporated herein by reference.

SUMMARY

Embodiments of the disclosure are directed to apparatuses and methodsfor ablating target tissue from within a vessel or other structure ofthe body. Embodiments of the disclosure are directed to apparatuses andmethods for ablating perivascular renal nerves from within the renalartery for the treatment of hypertension. Embodiments of the disclosureinclude a self-expanding cooling electrode configured to deliver highfrequency energy to innervated perivascular tissue adjacent a renalartery while providing protective cooling for the renal artery.Embodiments of a self-expanding cooling electrode include various tubearrangements constructed from metallic material that expands andcontracts in response to changes in temperature, and that provide forconcurrent self-expansion and protective cooling in response to areduction in electrode temperature lower than a neutral temperature,such as an ambient temperature of the human body.

In accordance with various embodiments, an apparatus includes a metallictube arrangement comprising an electrode region configured to expandradially and contract radially in response to increasing and decreasinga temperature at the electrode region, respectively. The electroderegion is configured for intravascular deployment and delivery of highfrequency energy to target tissue of a target vessel of the body. Theelectrode region is configured to expand radially to a diametersufficient to contact an inner wall of the target vessel in response toa decrease in electrode region temperature and to contract radially to adiameter smaller than a diameter of the target vessel in response to anincrease in electrode region temperature.

According to various embodiments, an apparatus includes a metallic tubearrangement comprising a proximal end, a distal end, an inlet, and anoutlet. The distal end comprises a coil section and the proximal endcomprises the inlet adapted to receive thermal transfer fluid. At leastthe coil section of the tube arrangement is dimensioned for deploymentwithin a target vessel. The coil section is configured to expandradially to a diameter sufficient to contact an inner wall of the targetvessel in response to receiving cooled thermal transfer fluid. At leasta portion of the coil section defines an electrode configured to deliverhigh frequency energy to target tissue. The proximal end of the metallictube arrangement is configured to electrically couple to an electricalenergy generator. The coil section is configured to contract radially toa diameter smaller than an inner wall of the target vessel in responseto removal of the cooled thermal transfer fluid via the outlet.

Various embodiments are directed to methods that involve supplyingthermal transfer fluid to a metallic tube arrangement positioned withina target vessel of the body. The tube arrangement comprises a coiledsection having a diameter that changes in response to changing atemperature of the thermal transfer fluid. Methods further involveincreasing the diameter of the coiled section such that portions of thecoiled section contact portions of the target vessel in response todecreasing the temperature of the thermal transfer fluid, deliveringhigh frequency energy to the target vessel from one or more electrodeportions of the tube arrangement while the coiled section portions arein contact with the target vessel portions, and decreasing the diameterof the coiled section to a diameter less than a diameter of the targetvessel in response to increasing the temperature of the thermal transferfluid.

These and other features can be understood in view of the followingdetailed discussion and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a right kidney and renal vasculatureincluding a renal artery branching laterally from the abdominal aorta;

FIGS. 2A and 2B illustrate sympathetic innervation of the renal artery;

FIG. 3A illustrates various tissue layers of the wall of the renalartery;

FIGS. 3B and 3C illustrate a portion of a renal nerve;

FIG. 4 shows an expandable cooling electrode adapted for renal nerveablation in a low-profile introduction configuration in accordance withvarious embodiments;

FIG. 5 shows an expandable cooling electrode adapted for renal nerveablation in an ablation configuration in accordance with variousembodiments;

FIGS. 6A through 6C show various aspects of an ablation apparatuscomprising an expandable cooling electrode extending from a distal endof a delivery sheath in accordance with various embodiments;

FIG. 7 shows a cross-section of a coiled section of an expandablecooling electrode having a thermal memory metallic tube construction inaccordance with various embodiments;

FIG. 8 shows a cross-section of a coiled section of an expandablecooling electrode having a bi-metallic tube construction in accordancewith various embodiments;

FIG. 9 shows a cross-section of a coiled section of an expandablecooling electrode having an asymmetric bi-layer tube construction inaccordance with various embodiments; and

FIG. 10 shows a representative RF renal therapy apparatus in accordancewith various embodiments.

DETAILED DISCRIPTION

Embodiments of the disclosure are directed to apparatuses and methodsfor improved vessel wall contact and control in ablation of targettissue, such as perivascular renal nerves for the control ofhypertension. Embodiments of the disclosure are directed to variousmethods of ablating tissue at a short distance while protecting closertissue. Embodiments of the disclosure are directed to methods ofconstructing a self-expanding tubular cooling RF electrode.

Maintaining good contact with a wall of the renal artery during ablationof perivascular renal nerves has been difficult. Conventional approachesoften have problems in obtaining good contact between an intravascularablation device and the artery wall, resulting in ineffective ablationof target nerves, or resulting in undesirable injury to arterial walltissue. If contact is variable, the tissue temperatures are not wellcontrolled, and an ablative temperature may not be achieved in thetarget tissue, while temperature in other areas, such as portions of theartery wall, may deviate enough to cause unwanted arterial tissueinjury. For ideal anatomy, good vessel apposition can be achieved moreeasily, but especially with tortuous or diseased renal arteries, therecan be very poor contact to effectively and predictably transfer heat,electrical current, or other energy from an ablation device to thetarget tissue.

Various embodiments are directed to ablation devices and methods thatprovide for improved vessel contact, as well as cooling the vessel atthe line of contact, for reduced vessel injury. According to someembodiments, an ablation apparatus includes a metallic coiled structurewhich expands when it is cooled. The expanded coiled structure makesgood contact with the vessel wall, and then portions of the coiledstructure are used as RF electrodes to deliver energy to the nearbytissues. The coiled structure preferably includes a coiled metallictube. Cooling fluid is passed through the coiled tube to concurrentlycause coil expansion and to cool and protect the vessel wall.

The cooled coiled structure prevents thermal injury to the vessel wherethe coiled structure contacts the vessel wall, while RF energy deliveredfrom the electrode(s) is propagated beyond the extent of the cooledregion. As such, a single coiled structure can provide improved vesselcontact, RF ablation of target tissue, and cooling for vessel wallprotection simultaneously.

Thermal memory metal tubing, for example, can be used for the coiledstructure. As the temperature is lowered or raised from a neutraltemperature, the coiled structure loosens or tightens, and moves outwardtoward the vessel wall or inward away from the vessel wall, depending onthe temperature. A cooled fluid can be passed through the coiledstructure, causing the coiled structure of the electrode to expandoutward toward the artery wall. The coiled structure can be adapted forphase-change cryothermal cooling by incorporating one or more orificesor narrowings to induce the phase change, or a simple cooled fluid canbe used since the amount of tissue to be cooled is relatively small.

The side of the coiled structure oriented away from the artery wall canbe insulated to reduce heat transfer from the blood, so that localvessel wall cooling and protection is more effective. When cooling ofthe coiled structure is terminated, the coiled structure deforms awayfrom the vessel wall, to form a lower profile for introduction orremoval of the device to and from the lumen of a target vessel. Afterdelivering the device into the lumen of the target vessel, the coiledstructure automatically self-deploys to achieve good vessel wall contactin response to cooling. After completion of an ablation procedure, thecoiled structure of the electrode returns to a low profile configurationwhen the cooling is terminated.

A return tube can be included in the construction of the coiledelectrode structure for handling spent cooling fluid. The return tubecan be a parallel coil, or a straight tube extending through the centerof the coiled structure, or other shape. A positioning sheath ispreferably provided for introduction and advancement of the coiledstructure within the vasculature. The self-expanding coiled structure iscoupled to an external control system which provides cooling fluid andRF energy to the coiled structure.

According to various embodiments, an expandable cooling structure whichincorporates a thermally activated RF electrode is constructed as anelongated tube having a length sufficient to extend between a patient'srenal artery and a percutaneous access location of the patient's body.Most of the elongated tube is preferably insulated and used to conductRF energy and cooling fluid to an expandable cooling electrode providedat the distal end of the elongated tube. Exposed portions of the coiledstructure act as an RF electrode(s) to deliver energy to innervatedperivascular renal tissue. The cooled coiled structure prevents thermalinjury to the renal artery where the coiled structure contacts the renalartery wall, while the RF energy is delivered farther from theelectrode(s) than the extent of the cooled region.

The coiled structure is preferably delivered into the lumen of the renalartery using a delivery sheath from an aortal access location. Thesheath can either be retracted from the coiled structure or the coiledstructure can be advanced out of the sheath's distal tip. The coiledstructure can be in direct contact with the artery wall, rather thancontained within a catheter balloon as in prior cryothermal approaches.This arrangement provides for improved wall contact for both cooling andRF ablation, and does not block blood flow within the renal artery. Thisallows the heating and cooling to be activated simultaneously and for anextended duration treatment if required. Using the various thermalshape-change structures disclosed herein, as the temperature is loweredor raised from a neutral temperature, the coiled structure loosens ortightens, and moves outward toward the artery wall or inward away fromthe artery wall, depending on the temperature.

Various embodiments of the disclosure are directed to apparatuses andmethods for renal denervation for treating hypertension. Hypertension isa chronic medical condition in which the blood pressure is elevated.Persistent hypertension is a significant risk factor associated with avariety of adverse medical conditions, including heart attacks, heartfailure, arterial aneurysms, and strokes. Persistent hypertension is aleading cause of chronic renal failure. Hyperactivity of the sympatheticnervous system serving the kidneys is associated with hypertension andits progression. Deactivation of nerves in the kidneys via renaldenervation can reduce blood pressure, and may be a viable treatmentoption for many patients with hypertension who do not respond toconventional drugs.

The kidneys are instrumental in a number of body processes, includingblood filtration, regulation of fluid balance, blood pressure control,electrolyte balance, and hormone production. One primary function of thekidneys is to remove toxins, mineral salts, and water from the blood toform urine. The kidneys receive about 20-25% of cardiac output throughthe renal arteries that branch left and right from the abdominal aorta,entering each kidney at the concave surface of the kidneys, the renalhilum.

Blood flows into the kidneys through the renal artery and the afferentarteriole, entering the filtration portion of the kidney, the renalcorpuscle. The renal corpuscle is composed of the glomerulus, a thicketof capillaries, surrounded by a fluid-filled, cup-like sac calledBowman's capsule. Solutes in the blood are filtered through the verythin capillary walls of the glomerulus due to the pressure gradient thatexists between the blood in the capillaries and the fluid in theBowman's capsule. The pressure gradient is controlled by the contractionor dilation of the arterioles. After filtration occurs, the filteredblood moves through the efferent arteriole and the peritubularcapillaries, converging in the interlobular veins, and finally exitingthe kidney through the renal vein.

Particles and fluid filtered from the blood move from the Bowman'scapsule through a number of tubules to a collecting duct. Urine isformed in the collecting duct and then exits through the ureter andbladder. The tubules are surrounded by the peritubular capillaries(containing the filtered blood). As the filtrate moves through thetubules and toward the collecting duct, nutrients, water, andelectrolytes, such as sodium and chloride, are reabsorbed into theblood.

The kidneys are innervated by the renal plexus which emanates primarilyfrom the aorticorenal ganglion. Renal ganglia are formed by the nervesof the renal plexus as the nerves follow along the course of the renalartery and into the kidney. The renal nerves are part of the autonomicnervous system which includes sympathetic and parasympatheticcomponents. The sympathetic nervous system is known to be the systemthat provides the bodies “fight or flight” response, whereas theparasympathetic nervous system provides the “rest and digest” response.Stimulation of sympathetic nerve activity triggers the sympatheticresponse which causes the kidneys to increase production of hormonesthat increase vasoconstriction and fluid retention. This process isreferred to as the renin-angiotensin-aldosterone-system (RAAS) responseto increased renal sympathetic nerve activity.

In response to a reduction in blood volume, the kidneys secrete renin,which stimulates the production of angiotensin. Angiotensin causes bloodvessels to constrict, resulting in increased blood pressure, and alsostimulates the secretion of the hormone aldosterone from the adrenalcortex. Aldosterone causes the tubules of the kidneys to increase thereabsorption of sodium and water, which increases the volume of fluid inthe body and blood pressure.

Congestive heart failure (CHF) is a condition that has been linked tokidney function. CHF occurs when the heart is unable to pump bloodeffectively throughout the body. When blood flow drops, renal functiondegrades because of insufficient perfusion of the blood within the renalcorpuscles. The decreased blood flow to the kidneys triggers an increasein sympathetic nervous system activity (i.e., the RAAS becomes tooactive) that causes the kidneys to secrete hormones that increase fluidretention and vasorestriction. Fluid retention and vasorestriction inturn increases the peripheral resistance of the circulatory system,placing an even greater load on the heart, which diminishes blood flowfurther. If the deterioration in cardiac and renal functioningcontinues, eventually the body becomes overwhelmed, and an episode ofheart failure decompensation occurs, often leading to hospitalization ofthe patient.

FIG. 1 is an illustration of a right kidney 10 and renal vasculatureincluding a renal artery 12 branching laterally from the abdominal aorta20. In FIG. 1, only the right kidney 10 is shown for purposes ofsimplicity of explanation, but reference will be made herein to bothright and left kidneys and associated renal vasculature and nervoussystem structures, all of which are contemplated within the context ofembodiments of the disclosure. The renal artery 12 is purposefully shownto be disproportionately larger than the right kidney 10 and abdominalaorta 20 in order to facilitate discussion of various features andembodiments of the present disclosure.

The right and left kidneys are supplied with blood from the right andleft renal arteries that branch from respective right and left lateralsurfaces of the abdominal aorta 20. Each of the right and left renalarteries is directed across the crus of the diaphragm, so as to formnearly a right angle with the abdominal aorta 20. The right and leftrenal arteries extend generally from the abdominal aorta 20 torespective renal sinuses proximate the hilum 17 of the kidneys, andbranch into segmental arteries and then interlobular arteries within thekidney 10. The interlobular arteries radiate outward, penetrating therenal capsule and extending through the renal columns between the renalpyramids. Typically, the kidneys receive about 20% of total cardiacoutput which, for normal persons, represents about 1200 mL of blood flowthrough the kidneys per minute.

The primary function of the kidneys is to maintain water and electrolytebalance for the body by controlling the production and concentration ofurine. In producing urine, the kidneys excrete wastes such as urea andammonium. The kidneys also control reabsorption of glucose and aminoacids, and are important in the production of hormones including vitaminD, renin and erythropoietin.

An important secondary function of the kidneys is to control metabolichomeostasis of the body. Controlling hemostatic functions includeregulating electrolytes, acid-base balance, and blood pressure. Forexample, the kidneys are responsible for regulating blood volume andpressure by adjusting volume of water lost in the urine and releasingerythropoietin and renin, for example. The kidneys also regulate plasmaion concentrations (e.g., sodium, potassium, chloride ions, and calciumion levels) by controlling the quantities lost in the urine and thesynthesis of calcitrol. Other hemostatic functions controlled by thekidneys include stabilizing blood pH by controlling loss of hydrogen andbicarbonate ions in the urine, conserving valuable nutrients bypreventing their excretion, and assisting the liver with detoxification.

Also shown in FIG. 1 is the right suprarenal gland 11, commonly referredto as the right adrenal gland. The suprarenal gland 11 is a star-shapedendocrine gland that rests on top of the kidney 10. The primary functionof the suprarenal glands (left and right) is to regulate the stressresponse of the body through the synthesis of corticosteroids andcatecholamines, including cortisol and adrenaline (epinephrine),respectively. Encompassing the kidneys 10, suprarenal glands 11, renalvessels 12, and adjacent perirenal fat is the renal fascia, e.g.,Gerota's fascia, (not shown), which is a fascial pouch derived fromextraperitoneal connective tissue.

The autonomic nervous system of the body controls involuntary actions ofthe smooth muscles in blood vessels, the digestive system, heart, andglands. The autonomic nervous system is divided into the sympatheticnervous system and the parasympathetic nervous system. In general terms,the parasympathetic nervous system prepares the body for rest bylowering heart rate, lowering blood pressure, and stimulating digestion.The sympathetic nervous system effectuates the body's fight-or-flightresponse by increasing heart rate, increasing blood pressure, andincreasing metabolism.

In the autonomic nervous system, fibers originating from the centralnervous system and extending to the various ganglia are referred to aspreganglionic fibers, while those extending from the ganglia to theeffector organ are referred to as postganglionic fibers. Activation ofthe sympathetic nervous system is effected through the release ofadrenaline (epinephrine) and to a lesser extent norepinephrine from thesuprarenal glands 11. This release of adrenaline is triggered by theneurotransmitter acetylcholine released from preganglionic sympatheticnerves.

The kidneys and ureters (not shown) are innervated by the renal nerves14. FIGS. 1 and 2A-2B illustrate sympathetic innervation of the renalvasculature, primarily innervation of the renal artery 12. The primaryfunctions of sympathetic innervation of the renal vasculature includeregulation of renal blood flow and pressure, stimulation of reninrelease, and direct stimulation of water and sodium ion reabsorption.

Most of the nerves innervating the renal vasculature are sympatheticpostganglionic fibers arising from the superior mesenteric ganglion 26.The renal nerves 14 extend generally axially along the renal arteries12, enter the kidneys 10 at the hilum 17, follow the branches of therenal arteries 12 within the kidney 10, and extend to individualnephrons. Other renal ganglia, such as the renal ganglia 24, superiormesenteric ganglion 26, the left and right aorticorenal ganglia 22, andceliac ganglia 28 also innervate the renal vasculature. The celiacganglion 28 is joined by the greater thoracic splanchnic nerve (greaterTSN). The aorticorenal ganglia 26 is joined by the lesser thoracicsplanchnic nerve (lesser TSN) and innervates the greater part of therenal plexus.

Sympathetic signals to the kidney 10 are communicated via innervatedrenal vasculature that originates primarily at spinal segments T10-T12and L1. Parasympathetic signals originate primarily at spinal segmentsS2-S4 and from the medulla oblongata of the lower brain. Sympatheticnerve traffic travels through the sympathetic trunk ganglia, where somemay synapse, while others synapse at the aorticorenal ganglion 22 (viathe lesser thoracic splanchnic nerve, i.e., lesser TSN) and the renalganglion 24 (via the least thoracic splanchnic nerve, i.e., least TSN).The postsynaptic sympathetic signals then travel along nerves 14 of therenal artery 12 to the kidney 10. Presynaptic parasympathetic signalstravel to sites near the kidney 10 before they synapse on or near thekidney 10.

With particular reference to FIG. 2A, the renal artery 12, as with mostarteries and arterioles, is lined with smooth muscle 34 that controlsthe diameter of the renal artery lumen 13. Smooth muscle, in general, isan involuntary non-striated muscle found within the media layer of largeand small arteries and veins, as well as various organs. The glomeruliof the kidneys, for example, contain a smooth muscle-like cell calledthe mesangial cell. Smooth muscle is fundamentally different fromskeletal muscle and cardiac muscle in terms of structure, function,excitation-contraction coupling, and mechanism of contraction.

Smooth muscle cells can be stimulated to contract or relax by theautonomic nervous system, but can also react on stimuli from neighboringcells and in response to hormones and blood borne electrolytes andagents (e.g., vasodilators or vasoconstrictors). Specialized smoothmuscle cells within the afferent arteriole of the juxtaglomerularapparatus of kidney 10, for example, produces renin which activates theangiotension II system.

The renal nerves 14 innervate the smooth muscle 34 of the renal arterywall 15 and extend lengthwise in a generally axial or longitudinalmanner along the renal artery wall 15. The smooth muscle 34 surroundsthe renal artery circumferentially, and extends lengthwise in adirection generally transverse to the longitudinal orientation of therenal nerves 14, as is depicted in FIG. 2B.

The smooth muscle 34 of the renal artery 12 is under involuntary controlof the autonomic nervous system. An increase in sympathetic activity,for example, tends to contract the smooth muscle 34, which reduces thediameter of the renal artery lumen 13 and decreases blood perfusion. Adecrease in sympathetic activity tends to cause the smooth muscle 34 torelax, resulting in vessel dilation and an increase in the renal arterylumen diameter and blood perfusion. Conversely, increasedparasympathetic activity tends to relax the smooth muscle 34, whiledecreased parasympathetic activity tends to cause smooth musclecontraction.

FIG. 3A shows a segment of a longitudinal cross-section through a renalartery, and illustrates various tissue layers of the wall 15 of therenal artery 12. The innermost layer of the renal artery 12 is theendothelium 30, which is the innermost layer of the intima 32 and issupported by an internal elastic membrane. The endothelium 30 is asingle layer of cells that contacts the blood flowing though the vessellumen 13. Endothelium cells are typically polygonal, oval, or fusiform,and have very distinct round or oval nuclei. Cells of the endothelium 30are involved in several vascular functions, including control of bloodpressure by way of vasoconstriction and vasodilation, blood clotting,and acting as a barrier layer between contents within the lumen 13 andsurrounding tissue, such as the membrane of the intima 32 separating theintima 32 from the media 34, and the adventitia 36. The membrane ormaceration of the intima 32 is a fine, transparent, colorless structurewhich is highly elastic, and commonly has a longitudinal corrugatedpattern.

Adjacent the intima 32 is the media 33, which is the middle layer of therenal artery 12. The media is made up of smooth muscle 34 and elastictissue. The media 33 can be readily identified by its color and by thetransverse arrangement of its fibers. More particularly, the media 33consists principally of bundles of smooth muscle fibers 34 arranged in athin plate-like manner or lamellae and disposed circularly around thearterial wall 15. The outermost layer of the renal artery wall 15 is theadventitia 36, which is made up of connective tissue. The adventitia 36includes fibroblast cells 38 that play an important role in woundhealing.

A perivascular region 37 is shown adjacent and peripheral to theadventitia 36 of the renal artery wall 15. A renal nerve 14 is shownproximate the adventitia 36 and passing through a portion of theperivascular region 37. The renal nerve 14 is shown extendingsubstantially longitudinally along the outer wall 15 of the renal artery12. The main trunk of the renal nerves 14 generally lies in or on theadventitia 36 of the renal artery 12, often passing through theperivascular region 37, with certain branches coursing into the media 33to enervate the renal artery smooth muscle 34.

Embodiments of the disclosure may be implemented to provide varyingdegrees of denervation therapy to innervated renal vasculature. Forexample, embodiments of the disclosure may provide for control of theextent and relative permanency of renal nerve impulse transmissioninterruption achieved by denervation therapy delivered using a treatmentapparatus of the disclosure. The extent and relative permanency of renalnerve injury may be tailored to achieve a desired reduction insympathetic nerve activity (including a partial or complete block) andto achieve a desired degree of permanency (including temporary orirreversible injury).

Returning to FIGS. 3B and 3C, the portion of the renal nerve 14 shown inFIGS. 3B and 3C includes bundles 14 a of nerve fibers 14 b eachcomprising axons or dendrites that originate or terminate on cell bodiesor neurons located in ganglia or on the spinal cord, or in the brain.Supporting tissue structures 14 c of the nerve 14 include theendoneurium (surrounding nerve axon fibers), perineurium (surroundsfiber groups to form a fascicle), and epineurium (binds fascicles intonerves), which serve to separate and support nerve fibers 14 b andbundles 14 a. In particular, the endoneurium, also referred to as theendoneurium tube or tubule, is a layer of delicate connective tissuethat encloses the myelin sheath of a nerve fiber 14 b within afasciculus.

Major components of a neuron include the soma, which is the central partof the neuron that includes the nucleus, cellular extensions calleddendrites, and axons, which are cable-like projections that carry nervesignals. The axon terminal contains synapses, which are specializedstructures where neurotransmitter chemicals are released in order tocommunicate with target tissues. The axons of many neurons of theperipheral nervous system are sheathed in myelin, which is formed by atype of glial cell known as Schwann cells. The myelinating Schwann cellsare wrapped around the axon, leaving the axolemma relatively uncoveredat regularly spaced nodes, called nodes of Ranvier. Myelination of axonsenables an especially rapid mode of electrical impulse propagationcalled saltation.

In some embodiments, a treatment apparatus of the disclosure may beimplemented to deliver denervation therapy that causes transient andreversible injury to renal nerve fibers 14 b. In other embodiments, atreatment apparatus of the disclosure may be implemented to deliverdenervation therapy that causes more severe injury to renal nerve fibers14 b, which may be reversible if the therapy is terminated in a timelymanner. In preferred embodiments, a treatment apparatus of thedisclosure may be implemented to deliver denervation therapy that causessevere and irreversible injury to renal nerve fibers 14 b, resulting inpermanent cessation of renal sympathetic nerve activity. For example, atreatment apparatus may be implemented to deliver a denervation therapythat disrupts nerve fiber morphology to a degree sufficient tophysically separate the endoneurium tube of the nerve fiber 14 b, whichcan prevent regeneration and re-innervation processes.

By way of example, and in accordance with Seddon's classification as isknown in the art, a treatment apparatus of the disclosure may beimplemented to deliver a denervation therapy that interrupts conductionof nerve impulses along the renal nerve fibers 14 b by imparting damageto the renal nerve fibers 14 b consistent with neruapraxia. Neurapraxiadescribes nerve damage in which there is no disruption of the nervefiber 14 b or its sheath. In this case, there is an interruption inconduction of the nerve impulse down the nerve fiber, with recoverytaking place within hours to months without true regeneration, asWallerian degeneration does not occur. Wallerian degeneration refers toa process in which the part of the axon separated from the neuron's cellnucleus degenerates. This process is also known as anterogradedegeneration. Neurapraxia is the mildest form of nerve injury that maybe imparted to renal nerve fibers 14 b by use of a treatment apparatusaccording to embodiments of the disclosure.

A treatment apparatus may be implemented to interrupt conduction ofnerve impulses along the renal nerve fibers 14 b by imparting damage tothe renal nerve fibers consistent with axonotmesis. Axonotmesis involvesloss of the relative continuity of the axon of a nerve fiber and itscovering of myelin, but preservation of the connective tissue frameworkof the nerve fiber. In this case, the encapsulating support tissue 14 cof the nerve fiber 14 b are preserved. Because axonal continuity islost, Wallerian degeneration occurs. Recovery from axonotmesis occursonly through regeneration of the axons, a process requiring time on theorder of several weeks or months. Electrically, the nerve fiber 14 bshows rapid and complete degeneration. Regeneration and re-innervationmay occur as long as the endoneural tubes are intact.

A treatment apparatus may be implemented to interrupt conduction ofnerve impulses along the renal nerve fibers 14 b by imparting damage tothe renal nerve fibers 14 b consistent with neurotmesis. Neurotmesis,according to Seddon's classification, is the most serious nerve injuryin the scheme. In this type of injury, both the nerve fiber 14 b and thenerve sheath are disrupted. While partial recovery may occur, completerecovery is not possible. Neurotmesis involves loss of continuity of theaxon and the encapsulating connective tissue 14 c, resulting in acomplete loss of autonomic function, in the case of renal nerve fibers14 b. If the nerve fiber 14 b has been completely divided, axonalregeneration causes a neuroma to form in the proximal stump.

A more stratified classification of neurotmesis nerve damage may befound by reference to the Sunderland System as is known in the art. TheSunderland System defines five degrees of nerve damage, the first two ofwhich correspond closely with neurapraxia and axonotmesis of Seddon'sclassification. The latter three Sunderland System classificationsdescribe different levels of neurotmesis nerve damage.

The first and second degrees of nerve injury in the Sunderland systemare analogous to Seddon's neurapraxia and axonotmesis, respectively.Third degree nerve injury, according to the Sunderland System, involvesdisruption of the endoneurium, with the epineurium and perineuriumremaining intact. Recovery may range from poor to complete depending onthe degree of intrafascicular fibrosis. A fourth degree nerve injuryinvolves interruption of all neural and supporting elements, with theepineurium remaining intact. The nerve is usually enlarged. Fifth degreenerve injury involves complete transection of the nerve fiber 14 b withloss of continuity.

Turning now to FIGS. 4 and 5, there is illustrated a self-expandingcooling electrode 100 adapted for renal nerve ablation in accordancewith various embodiments. FIG. 4 shows an expandable cooling electrode100 in a low-profile introduction configuration. When in the low-profileintroduction configuration, the expandable cooling electrode 100 can bedeployed within the lumen of a target vessel, such as a patient's renalartery, or other structure of the body. FIG. 5 shows the coolingelectrode 100 in an expanded ablation configuration. When in theablation configuration, the expandable cooling electrode 100 ispreferably used to deliver high frequency energy (e.g., RF current) totarget tissue of the vessel or other body tissue of interest.

According to various embodiments, and as shown in FIG. 4, an expandablecooling electrode 100 is constructed as a metallic tube 101 having aproximal and 102, a distal end 104, and a coil section 106 definedbetween the proximal and distal ends 102 and 104. The metallic tube 101is shown having a generally elongated configuration with a portion ofthe metallic tube 101 wrapped around itself to form the coiled section106. At the proximal end 102, an inlet 110 and an outlet 112 of themetallic tube 101 are aligned in a co-parallel relationship. As such,access to both the inlet 110 and the outlet 112 of the metallic tube 101are accessible from the proximal end 102.

It is understood that the metallic tube 101 can be formed to assume avariety of configurations, and that those configurations shown in thedrawings represent non-limiting examples of various embodiments. Forexample, the expandable cooling electrode 100 is shown in FIGS. 4 and 5to include a supply tube 111 and a return tube 113. As illustrated, thedistal end of the supply tube 111 includes the coiled section 106wrapped around the return tube 113 which is shown to be a straight tubeextending through the center of the coiled section 106. In someembodiments, the return tube 113 can be shaped to include a coiledsection aligned in a co-parallel relationship with the coiled section106 of the supply tube 111. In other embodiments, the return tube 113need not be co-parallel with the supply tube 111 nor extend to theproximal end 102. For example, the outlet 112 can be located anywheredistal of the coiled section 106, such as at a location suited forexpelling spent biocompatible thermal transfer fluid from the metallictube 101 and into blood flowing past the metallic tube.

The supply and return tubes 111 and 113 include lumens through which athermal transfer fluid can be transported. The materials used tofabricate the coiled section 106 of the metallic tube 101 allow thediameter of the coiled section 106 to change in response to changes intemperature. In preferred embodiments, the diameter of the coiledsection 106 increases in response to cooling relative to ambient or aneutral temperature (e.g., body temperature), and decreases in responseto warming relative to ambient or a neutral temperature. For example, asthe temperature of the coiled section 106 is lowered or raised relativeto a neutral temperature, the coiled section 106 loosens or tightens,and moves outwardly toward the vessel wall or inwardly away from thevessel wall, depending on the temperature.

According to various embodiments, the coiled section 106 of the metallictube 101 can be formed from thermal memory metal tubing, bi-metallictubing, bi-layer tubing, or other metallic tubing that undergoes a shapechange in response to changes in temperature. Metallic materials used toform the coiled section 106 preferably have a negative thermalcoefficient of expansion. More preferably, suitable metallic materialsthat can be used to construct the coiled section 106 includes those thathave a linear negative thermal coefficient of expansion, in which thematerial's linear dimension changes as a function of temperature change(e.g., the fractional change in length per degree of temperaturechange). Portions of the metallic tube 101 proximal and distal to thecoiled section 106 are preferably formed from metal or metal alloys thatnegligibly change shape in response to changes in temperature.

In the introduction configuration shown in FIG. 4, the coiled section106 of the metallic tube 101 has a diameter of D₁. The introductiondiameter, D₁, is preferably selected so that the expandable coolingelectrode 100 can be readily and safely deployed in the lumen of atarget vessel of the body, such as a renal artery. By way of example,and in the context of renal nerve ablation, the coiled section 106 mayhave an introduction diameter, D₁, of about 1 mm to about 2.5 mm. In theablation configuration shown in FIG. 5, the coiled section 106 of themetallic tube 101 has a diameter of D₂. The expanded diameter, D₂, ispreferably selected so that the coiled section 106 makes contact with aninner wall of the target vessel. In the context of renal nerve ablation,for example, the coiled section 106 may have an expanded diameter, D₂,of about 4 mm to about 8 mm. In various applications, the diameter ofthe coiled section 106 in its ablation configuration can increasebetween about 200% and about 800% relative to its introductionconfiguration.

Desired thermal response characteristics of the coiled section 106, suchas the degree and/or timeliness of expansion and contraction, can bedesigned into the coiled section 106 depending on applicationparticulars and the type of thermal transfer fluid used to cool thecoiled section 106. A variety of thermal transfer fluids may beemployed, including cold saline or cold saline and ethanol mixture,Freon or other fluorocarbon refrigerants, nitrous oxide, liquidnitrogen, and liquid carbon dioxide, for example. In some embodiments, acooled thermal transfer fluid may be supplied by an external fluidsource, circulated through the coiled section 106, and spent thermaltransfer fluid returned to the external fluid source. In otherembodiments, a cooled biocompatible thermal transfer fluid may besupplied by an external fluid source, circulated through the coiledsection 106, and expelled into blood flowing through a target vessel,such as a renal artery.

According to some embodiments, the metallic tube 101 can be constructedto provide phase-change cryothermal cooling by incorporating one or moreorifices or narrowings to induce the phase change at the coiled section106. A liquid cryogen, for example, can be supplied to the metallic tube101 through inlet 110. When released inside the coiled section 106, theliquid cryogen undergoes a phase change that cools the coiled section106 by absorbing the latent heat of vaporization from the surroundingtissue, and by cooling of the vaporized gas as it enters a region oflower pressure inside the coiled section 106 (via the Joule-Thomsoneffect). The gas released inside the distal portion of the coiledsection 106 is exhausted through outlet 112. The pressure inside thecoiled section 106 may be controlled by regulating one or both of a rateat which cryogen is delivered and a rate at which the exhaust gas isextracted.

One or more temperature sensors may be provided at the coiled section106 for measuring tube and/or arterial tissue temperature. One or moreconductors can be used for coupling each of the temperature sensors toan external temperature unit.

A desired degree of shape change of the coiled section 106 can beachieved using different construction techniques and materials. Theextent of shape change of the coiled section 106 can be induced overdifferent temperature ranges, such as a relatively small temperaturerange or a relatively large temperature range. The change in shape ofthe coiled section 106 may be uniform or asymmetric depending on theconstruction of the coiled section 106. Other properties andcharacteristics can be designed into the metallic tube 101 and coiledsection 106, such as flexibility, depending on the particular targetvessel or other target structures of the body.

According to various embodiments, at least the coiled section 106 of themetallic tube 101 defines an electrode adapted to ablate target tissueof a target vessel, such as innervated perivascular tissue surrounding apatient's renal artery. All or a portion of the metallic tube 101, suchas the coiled section 106, is preferably left exposed so that theexposed portion or portions of the metallic tube 101 define an ablationelectrode, which electrically cooperates with another electrode duringablation. In some embodiments, the other electrode comprises an externalpad electrode of an external generator, such as an RF generator. In suchembodiments, the exposed portion(s) of the metallic tube 101 and theexternal electrode are operated in a monopolar configuration. Accordingto other embodiments, the other electrode can be placed within the bodyin proximity to the exposed portion of the metallic tube 101. Forexample, the other electrode can be placed within a renal vein inproximity to the renal artery in which the expandable cooling electrode100 is situated.

The helical shape of the expandable cooling electrode 100 allows aspiral region of perivascular renal nerve tissue to be ablated toachieve termination of renal sympathetic nerve activity in a reducedamount of time relative to conventional approaches and with minimal orno injury to the renal artery. The expandable cooling electrode 100advantageously provides for delivery of high frequency energy forablating perivascular renal nerve tissue and simultaneous cooling toprevent thermal damage to the renal artery wall. The thermal mechanismused to cause expansion of the coiled section 106 of the expandablecooling electrode 100 also provides protective cooling for the renalartery wall. For example, the expandable cooling electrode 100 can bedeployed within the lumen of a renal artery in its introductionconfiguration, cooled to cause expansion of the coiled section 106 toits ablation configuration, and energized to ablate at least a 360°spiral of innervated perivascular renal tissue without having toreposition the electrode 100 during the ablation procedure and withoutthermally injuring the renal artery wall.

FIGS. 6A through 6C show various aspects of an ablation apparatus inaccordance with various embodiments. FIGS. 6A-6C show an ablationcatheter 105 comprising a sheath 90 and an expandable cooling electrode100 extending from a distal end of the sheath 90. The sheath 90 is shownto extend into the ostium of the renal artery 12 accessed from the aorta20 inferior to the renal artery 12. The sheath 90 includes a lumen 92dimensioned to receive the expandable cooling electrode arrangement inits introduction configuration. The sheath 90 typically has a lengthsufficient to access a target vessel, such as the renal artery 12, froma perivascular access location of the patient.

The expandable cooling electrode 100 is shown coupled to a tubearrangement 103 which includes supply and return tubes 111 and 113 thatrespectively extend along the length of the sheath 90. The distal endsof supply and return tubes 111 and 113 are fluidly coupled to inlet 110and outlet 112 of the metallic tube 101, respectively. The proximal endsof the supply and return tubes 111 and 113 are preferably configured tofluidly coupled to supply and return couplings of an external thermaltransfer fluid source. The proximal ends of the supply and return tubes111 and 113 are electrically coupled to an external energy source, suchas an RF generator. In order to electrically insulate the proximal endsof the supply and return tubes 111 and 113 from the external thermaltransfer fluid source, non-metallic fluid couplings are preferably usedto fluidly coupled the proximal ends of the supply and return tubes 111and 113 to supply and return lines of the external thermal transferfluid source.

The supply and return tubes 111 and 113 are preferably covered withinsulation to electrically and thermally isolate the two tubes 111 and113 from each other. The inner lumen 92 of the sheath 90 may alsoinclude insulation to prevent cooled thermal transfer fluid transportedthrough the supply tube 111 from warming due to ambient heat produced bythe body. In some embodiments, a low-conductivity fluid is used to limitundesired electrical pathways.

According to other embodiments, the supply and return tubes 111 113 neednot be metallic. Electrically non-conductive supply and return tubes 111and 113 can be fluidly coupled to inlet 110 and outlet 112 of themetallic tube 101. According to such embodiments, an electricalconductor extends along the length of the sheath 102 and electricallycouples the metallic tube 101 at its proximal end 102 with an externalenergy source. The electrical conductor can be supported on orencompassed within a lumen of the non-conductive supply tube 111 orreturn tube 113.

FIG. 7 shows a cross-section of the coiled section 106 of the metallictube 101 having a thermal memory metallic tube construction inaccordance with various embodiments. In the embodiment shown in FIG. 7,the coiled section 106 is formed from a thermal memory metallic tube 122having a lumen 123 through which thermal transfer fluid can betransported. The thermal memory metallic material used to form tube 122of the coiled section 106 typically provides shape change over arelatively small temperature range. For example, suitable thermal memorymetallic materials that provides for shape change over a relativelysmall temperature range include some alloys of nickel-titanium(nitinol), copper-zinc-aluminum-nickel, copper-aluminum-nickel, and somealloys of zinc, copper, gold and iron. These and other suitable thermalmemory metallic materials can provide shape change over a temperaturerange of about 5° C., with transition chosen in the temperature range ofabout −10° C. to about +30° C. for this application, with about a 10° C.temperature hysteresis.

FIG. 7 further shows insulation 124 covering an outer region of themetallic tube 122 which is exposed to blood flowing in the targetvessel. The insulation 124, which is an optional feature, thermallyinsulates the side of the coiled section 106 oriented away from thevessel wall in order to reduce heat transfer from blood, so that localvessel wall cooling and protection is enhanced.

FIG. 8 shows a cross-section of the coiled section 106 of the metallictube 101 having a bi-metallic tube construction in accordance withvarious embodiments. The embodiment shown in FIG. 8 includes a metallictube 101 constructed as a two-sided bi-metallic tube 101. Thebi-metallic tube 126 of the coiled section 106 is preferably formed byincorporating two metals 126 a and 126 b having differing thermalexpansion properties. According to some embodiments, a first metal 126 ais used to form half of the circumference of the bi-metallic tube 101,and a second metal 126 b is used to form the other half of thecircumference of the bi-metallic tube 101. The first and second metals126 a and 126 b have differing thermal expansion properties. The twohalves are welded or otherwise bonded to one another to form thebi-metallic tube structure 126 of the coiled section 106. Thebi-metallic tube 126 may include insulation 124 to thermally insulatethe side of the coiled section 106 oriented away from the vessel wallfor reasons previously discussed.

Use of bi-metallic tubing 126 in the construction of the coiled section106 provides for a shape change of the coiled section 106 over arelatively large temperature range as compared to the thermal memorymetallic material used to form tube 122 in the embodiment shown in FIG.7. For example, suitable metals having differing thermal expansionproperties that can be used to fabricate the bi-metallic tube 126 of thecoiled section 106 include stainless steel and copper. These and othersuitable bi-metallic metals can provide a gradual shape change over aseveral hundred degree temperature range, but the coiled section 106 canbe designed to achieve the desired shape change resulting fromtemperature changes of about 10° C. to about 30° C. The practicaltemperature range is to stay above cryothermal injury temperatures,(about −10° C. or so) and below body temperature (about 37° C. or so). Asmaller temperature range can be used so that the cooling required foractuating the coil is more easily achieved.

According to some embodiments, and depending on particulars of aspecific application, an intravascular device of the type describedabove (and elsewhere) can be fabricated using metal tubing having aninner diameter that ranges between about 0.003″ and 0.012″, and outerdiameter that ranges between about 0.006″ and 0.018″, and a wallthickness that ranges between about 0.0015″ and 0.005″.

In accordance with various embodiments, a polymer element or tube may beused in combination with a metal tube or a polymer element in theconstruction of the coiled section 106 (and other sections if desired).In some embodiments, the coiled section 106 is constructed using apolymer tube and a metal tube or element. In other embodiments, thecoiled section 106 excludes a metal tube or element, and uses acombination of a polymeric tube and a polymer element. For example, apolymer tube may be used with an asymmetric metal or polymer element sothat, due to differing thermal expansion properties, the polymer tubebends and straightens when heat is applied and removed. According tosome configurations, the polymer tube can be somewhat larger in diameterand in wall thickness since the stiffness (which is usually thepractical limit on size) is lower for polymers than for metal tubes.

FIG. 9 shows a cross-section of the coiled section 106 of the metallictube 101 having an asymmetric bi-layer metallic tube construction inaccordance with various embodiments. In the embodiment shown in FIG. 9,the coil section 106 comprises asymmetric walled tubing 128 with atleast two layers of metals 128 a and 128 b having differing thermalexpansion properties. According to some embodiments, a first tube 128 ais formed from a first metal and includes a lumen 120 through which athermal transfer fluid can be transported. The first tube 128 a isformed to have an asymmetric wall thickness. A second tube 128 b isformed from a second metal. The second tube 128 b is formed to have anasymmetric wall thickness and a lumen dimensioned to receive the firsttube 128 b. The dimensions of the first and second tubes 128 a and 128b, including wall thicknesses, can be selected to achieve desiredexpansion and shape change attributes.

A bonding material may be used to secure the first and second tubes 128a and 128 b together, although frictional forces between the two tubes128 a and 128 b may provide sufficient bonding. The asymmetric walledtubing 128 may include insulation 124 to thermally insulate the side ofthe coiled section 106 oriented away from the vessel wall for reasonspreviously discussed.

According to various embodiments, the thickest portion of the asymmetricwalls of the first and second tubes 128 a and 128 b can be oriented inopposition to one another as is shown in FIG. 9. The orientation of theasymmetrical walls of the first and second tubes 128 a and 128 b shownin FIG. 9 maximizes the extent of shape change of the coiled section 106in response to temperature changes. Suitable metals having differingthermal expansion properties that can be used to fabricate theasymmetric bi-layer metallic tube 128 shown in FIG. 9 include thosediscussed above with regard to the embodiments of FIG. 8, for example.

FIG. 10 shows a representative RF renal therapy apparatus 300 inaccordance with various embodiments of the disclosure. The apparatus 300illustrated in FIG. 10 includes external electrode activation circuitry320 which comprises power control circuitry 322 and timing controlcircuitry 324. The external electrode activation circuitry 320, whichincludes an RF generator, is coupled to temperature measuring circuitry328 and may be coupled to an optional impedance sensor 326. An ablationcatheter 105 of the RF renal therapy apparatus 300 includes a shaft 90having a lumen 92 configured to receive an expandable cooling electrode100 of a type previously described. FIG. 10 shows the coiled section 106of the expandable cooling electrode 100 deployed within a patient'srenal artery 12 in its ablation configuration.

The RF generator of the external electrode activation circuitry 320preferably includes a pad electrode 330 that is configured tocomfortably engage the patient's back or other portion of the body nearthe kidneys. Radiofrequency energy produced by the RF generator iscoupled to the expandable cooling electrode 100 by supply and/or returntubes of the expandable cooling electrode 100 or other conductorarrangement.

Renal denervation therapy using the apparatus shown in FIG. 10 istypically performed using the expandable cooling electrode 100 and thepad electrode 330 coupled to the RF generator 320, with the RF generator320 operating in a monopolar mode. The radiofrequency energy flowsthrough the expandable cooling electrode 100 and perivascular spaceadjacent the renal artery in accordance with a predetermined activationsequence to ablate perivascular tissue which includes renal nerves.

In general, when renal artery tissue temperatures rise above about 113°F. (50° C.), protein is permanently damaged (including those of renalnerve fibers). If heated over about 65° C., collagen denatures andtissue shrinks If heated over about 65° C. and up to 100° C., cell wallsbreak and oil separates from water. Above about 100° C., tissuedesiccates.

According to some embodiments, the electrode activation circuitry 320 isconfigured to control activation and deactivation of the expandablecooling electrode 100 in accordance with a predetermined energy deliveryprotocol and in response to signals received from temperature measuringcircuitry 328. The electrode activation circuitry 320 controlsradiofrequency energy delivered to the expandable cooling electrode 100so as to maintain the current densities at a level sufficient to causeheating of the perivascular renal tissue to at least a temperature of55° C.

Temperature sensors can be situated at the expandable cooling electrode100 to provide continuous monitoring of renal artery tissuetemperatures, and RF generator power can be automatically adjusted sothat target temperatures are achieved and maintained. An impedancesensor arrangement 326 may be used to measure and monitor electricalimpedance during RF denervation therapy, and the power and timing of theRF generator 320 may be moderated based on the impedance measurements ora combination of impedance and temperature measurements.

Marker bands 314 can be placed on one or multiple parts of theexpandable cooling electrode 100 and/or sheath 90 to enablevisualization during the procedure. A guidewire can be used to locatethe renal artery to be treated, and the sheath 90 can be advanced overthe guidewire and to or through the ostium of the renal artery. A hingemechanism 356, such as a slotted tube portion of the sheath 90, can bebuilt into the distal end of the sheath 90 to facilitate navigation ofthe near 90° turn from the aorta into the renal artery 12. Theexpandable cooling electrode 100 can then be advanced through the sheath90 and into the renal artery.

The embodiments shown in the figures have been generally described inthe context of intravascular-based ablation of perivascular renal nervesfor control of hypertension. It is understood, however, that embodimentsof the disclosure have applicability in other contexts, such as energydelivery and cooling from within other vessels of the body, includingother arteries, veins, and vasculature (e.g., cardiac and urinaryvasculature and vessels), and other tissues of the body, includingvarious organs. For example, a self-expanding cooling electrode can beconfigured for deployment within the renal vein, and another electrodecan be situated externally of the renal vein (e.g., within or near thetarget renal artery) or the patient. An appropriately sizedself-expanding cooling electrode can be deployed in a cardiac chamber,such as the right atrium for treating reentrant tachyarrhythmias, or acardiac vessel, such as the ostium of the pulmonary vein for treatingatrial fibrillation. By way of further example, various embodiments maybe configured for deployment in the urethra to treat benign prostatichyperplasia (BPH) or to treat a tumor using an appropriately sizedself-expanding cooling electrode of a type described hereinabove.

It is to be understood that even though numerous characteristics ofvarious embodiments have been set forth in the foregoing description,together with details of the structure and function of variousembodiments, this detailed description is illustrative only, and changesmay be made in detail, especially in matters of structure andarrangements of parts illustrated by the various embodiments to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

1. An apparatus, comprising: a metallic tube arrangement comprising aproximal end, a distal end, an inlet, and an outlet, the distal endcomprising a coil section and the proximal end comprising the inletadapted to receive thermal transfer fluid, at least the coil sectiondimensioned for deployment within a target vessel; the coil sectionconfigured to expand radially to a diameter sufficient to contact aninner wall of the target vessel in response to receiving cooled thermaltransfer fluid; at least a portion of the coil section defining anelectrode configured to deliver high frequency energy to target tissue,the proximal end of the metallic tube arrangement configured toelectrically couple to an electrical energy generator; and the coilsection configured to contract radially to a diameter smaller than aninner wall of the target vessel in response to removal of the cooledthermal transfer fluid via the outlet.
 2. The apparatus of claim 1,comprising a sheath comprising a flexible shaft having a proximal end, adistal end, a length, and a lumen extending between the proximal anddistal ends, the length of the shaft sufficient to access the targetvessel from a percutaneous access location, and the lumen dimensioned toreceive the metallic tube arrangement.
 3. The apparatus of claim 1,wherein: the coil section is configured to deliver high frequency energyto the target tissue sufficient to ablate the target tissue; and thecoil section is configured to receive the cooled thermal transfer fluidat a temperature that provides protective cooling to the inner wall ofthe target vessel and that causes radial expansion of the coil section.4. The apparatus of claim 1, wherein the target vessel comprises a renalartery, and the target tissue comprises perivascular tissue includingrenal nerves.
 5. The apparatus of claim 1, comprising: a supply tubefluidly coupled to the inlet of the tube arrangement and having a lengthof the shaft sufficient to access the target vessel from thepercutaneous access location; and a return tube fluidly coupled to theoutlet of the tube arrangement and having a length of the shaftsufficient to access the target vessel from the percutaneous accesslocation.
 6. The apparatus of claim 1, wherein: the thermal transferfluid comprises a biocompatible thermal transfer fluid; and the outletof the tube arrangement is adapted to expel spent biocompatible thermaltransfer fluid into blood flowing through the target vessel.
 7. Theapparatus of claim 1, wherein the tube arrangement comprises aphase-change cryothermal cooling arrangement.
 8. The apparatus of claim1, wherein the coil section is formed of a single layer of a thermalmemory alloy.
 9. The apparatus of claim 1, wherein the coil sectiondefines a two-sided bimetallic structure.
 10. The apparatus of claim 1,wherein the coil section comprises asymmetric walled tubing with atleast two layers of metals having differing thermal expansionproperties.
 11. The apparatus of claim 1, wherein the coil sectioncomprises thermal insulation covering portions of the coil sectionfacing away from the inner wall of the target vessel.
 12. The apparatusof claim 1, wherein the electrode is configured to deliverradiofrequency energy to the target tissue.
 13. The apparatus of claim1, wherein the coil section comprises one or more insulated sections andone or more exposed sections, the one or more exposed sections definingone or more electrodes.
 14. An apparatus, comprising: a metallic tubearrangement comprising an electrode region configured to expand radiallyand contract radially in response to increasing and decreasing atemperature at the electrode region, respectively, the electrode regionconfigured for intravascular deployment and delivery of high frequencyenergy to target tissue of a target vessel of the body; the electroderegion configured to expand radially to a diameter sufficient to contactan inner wall of the target vessel in response to a decrease inelectrode region temperature; and the electrode region configured tocontract radially to a diameter smaller than a diameter of the targetvessel in response to an increase in electrode region temperature. 15.The apparatus of claim 14, comprising a sheath comprising a flexibleshaft having a proximal end, a distal end, a length, and a lumenextending between the proximal and distal ends, the length of the shaftsufficient to access the target vessel from a percutaneous accesslocation, and the lumen dimensioned to receive the metallic tubearrangement.
 16. The apparatus of claim 14, wherein: the electroderegion comprises a fluid channel; the electrode region configured toexpand radially to the diameter sufficient to contact the inner wall ofthe target vessel in response to communicating cooled thermal transferfluid through the fluid channel; and the electrode region configured tocontract radially to the diameter smaller than the target vesseldiameter in response to terminating communication of cooled thermaltransfer fluid through the fluid channel.
 17. The apparatus of claim 14,wherein: the electrode region is configured to deliver high frequencyenergy to the target tissue sufficient to ablate the target tissue; andthe electrode region is configured to provide protective cooling to theinner wall of the target vessel.
 18. The apparatus of claim 14, whereinthe target vessel comprises a renal artery, and the target tissuecomprises perivascular tissue including renal nerves.
 19. A method,comprising: with a metallic tube arrangement comprising a coiled sectionpositioned within a target vessel of the body, supplying thermaltransfer fluid to the tube arrangement, the coiled section having adiameter that changes in response to changing a temperature of thethermal transfer fluid; increasing the diameter of the coiled sectionsuch that portions of the coiled section contact portions of the targetvessel in response to decreasing the temperature of the thermal transferfluid; delivering high frequency energy to the target vessel from one ormore electrode portions of the tube arrangement while the coiled sectionportions are in contact with the target vessel portions; and decreasingthe diameter of the coiled section to a diameter less than a diameter ofthe target vessel in response to increasing the temperature of thethermal transfer fluid.
 20. The method of claim 19, comprising returningspent thermal transfer fluid to a location external of the body.
 21. Themethod of claim 19, comprising expelling spent thermal transfer fluid toblood flowing through the target vessel.
 22. The method of claim 19,comprising advancing the tube arrangement through a sheath extendingfrom a percutaneous access location to the target vessel.